Pozzolans of various particular kinds are known in the prior art as being useful as performance-enhancing additives for cement, mortar, grout, stucco and concrete. Unless otherwise indicated, the term “cement” is used herein to refer collectively to cement, mortar, grout and stucco and “concrete” is used to refer to a mixture of an aggregate with a cement. Though pozzolans by themselves are generally of little, if any, use as a cement, the addition of pozzolans to either common or hydraulic portland cement enhances both the initial and long term physical properties of the cement. Pozzolans continue to participate in bond-forming reactions react in cement for many years, further strengthening the concrete and making it harder and more durable as time passes. Pozzolans also serve to densify and reduce water permeability of cured concrete thereby making the cement or concrete more resistant to deterioration and swelling caused by exposure to various conditions.
A pozzolan is a siliceous, or siliceous and aluminous, substance which will react at ordinary temperatures with calcium hydroxide formed during the hydration of cement to create additional cementitious material in the form of dicalcium and tricalcium silicate and calcium silico-aluminate hydrates. The American Society for the Testing and Materials Standard ASTM C-618, entitled “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use As a Mineral Admixture in Concrete” defines various classes of pozzolans. For example, a Class “N” Pozzolan are defined therein as “raw or calcined natural pozzolans that comply with the applicable requirements for the class as given herein, such as some diatomaceous earths; opaline cherts and shales; tuffs and volcanic ashes or pumices, calcined or uncalcined: and various materials requiring calcination to induce satisfactory properties, such as some clays and shales.” Class F Fly Ash is defined as “fly ash normally produced from burning anthracite or bituminous coal that meets the applicable requirements for this class as given herein. This class of fly ash has pozzolanic properties.” Class C Fly Ash is defined as “fly ash normally produced from lignite or sub-bituminous coal that meets the applicable requirements for this class as given herein treated this class of fly ash, in addition to having pozzolanic properties, also has some cementitious properties.”
Portland cement is a fine powder produced by grinding portland cement clinker. The major raw material for making portland cement clinker is a mixture of calcium carbonate (CaCO3), usually in the form of crushed limestone, and materials containing clay as a source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. Some of the secondary raw materials which can be incorporated in the mixture for making clinker are: clay, shale, sand, iron ore, bauxite, fly ash and slag. The raw mixture is heated in a cement kiln, a slowly rotating and sloped cylinder, with temperatures increasing over the length of the cylinder up to a peak temperature of about 1400-1450° C. A complex succession of chemical reactions take place as the temperature rises. The resulting clinker is a hydraulic material which consists of at least two-thirds by mass of dicalcium and tricalcium silicates (3CaO.SiO2 and 2CaO.SiO2) with the balance consisting mainly of aluminum-containing, and iron-containing, clinker phases and other compounds. The aluminum oxide and iron oxide are present as a flux and contribute little to concrete strength.
Due to the high temperature needed, the production of portland cement clinker requires large amounts of energy. The enthalpy of formation of clinker from calcium carbonate and clay minerals is about 7.1 MBTU per ton. However, because of heat loss inherent in actual production processes, the total heat input required can be much higher. The high energy requirements and the liberation of significant amounts of carbon dioxide in the course of generating the energy necessary to satisfy production requirements make cement production a significant source of carbon dioxide (CO2) emissions. CO2 release to the atmosphere on the order of 1.1 tons per ton of cement is not atypical. It has been estimated that portland cement production may account for as much as 5% of CO2 emissions worldwide.
The incorporation of certain types of pozzolans in cement is known in the art. For example, standard ASTM C-150 classifies portland cements as one of five basic types. The first three types allow for specific pozzolan additions in accordance with overall chemical and physical performance criteria. For example, “Type I” is considered common, or general purpose, portland cement. It is typically used for general construction and is especially useful for making precast and precast-pre-stressed concrete members that are not to be used in contact with soils or ground water. Using cement industry notation, a typical composition of a Type I portland cement is: 55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1% free (CaO). Type II cement is intended to have moderate sulfate resistance with or without moderate heat of hydration and is suitable for general use in contact with ground water exposed to moderate sulfide attack. A typical composition of a Type II portland cement would be 51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 1% free (CaO) with C3A not exceeding shall not exceed 8% and (C3A+C3S) not exceeding 58%. Type III portland cement exhibits relatively high early strength. A typical composition thereof is: 57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 1.3% free (CaO). A Type IV portland cement is slow curing and is generally known for its low heat of hydration. A typical composition of Type IV is: 28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.8% free (CaO) with C3A not in excess of 7% and C3S not in excess of 35%. Type V portland cements are typically used where sulfate resistance is important, such as applications with exposure to high alkali soil and/or sulfate groundwater. A typical Type V composition is: 38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.8% free (CaO) with C3A>2% and (2C3A+C4AF) not in excess of 20%.
ASTM C-1157 deals with hydraulic cements. That standard does not impose restrictions the chemical composition of the cement itself or its additives. Rather, it establishes standards of physical performance indicating the suitability of a cement for particular applications. For example:
Type GU—General Purpose cement
Type HE—High Early-Strength
Type MS—Moderate Sulfate Resistance
Type HS—High Sulfate Resistance.
Type MH—Moderate Heat of Hydration.
Type LH—Low Heat of Hydration.
ASTM Standard C-595 sets forth specifications for five classes of blended hydraulic cements for general and special application, using slags, pozzolans, or both, blended with portland cement.
Type IS—Portland/Blast Furnace Slag Cement—includes 25% to 70% blast furnace slag.
Type IP & P—Portland/Pozzolan cement—includes 15 to 40% pozzolan blended with either portland cement or Type IS cement.
Type I (PM)—Pozzolan modified portland cement—includes <15% Pozzolan blended with either portland cement or Type IS cement.
Type S—Slag cement>70% blast furnace slag ASTM C 989 blended with either portland cement or hydrated lime.
Types IA, IIA, and IIIA are the same as I, II, and III with the addition of air-entraining additives. Similarly, suffix MS is used to indicate moderate sulfide resistance, and suffix MH us to indicate moderate heat of hydration. Other suffixes are used to indicate subtypes exhibiting other particular properties.
ASTM Standards ASTM C-150, ASTM C-465, ASTM C-595, ASTM C-618, ASTM C-989 and ASTM C-1157 are expressly incorporated herein in their entireties to form part of the present disclosure.
U.S. Pat. No. 6,776,838 describes a white pozzolan, and a cement incorporating white pozzolan derived from byproducts of manufacturing vitreous low alkali, low iron, glass fibers such as those used for example and fiberglass thermal insulation. Bundles all of entangled strands of waste glass fibers are adjusted for moisture content, shredded, ground, and classified to control maximum particle size, particle distribution and aspect ratio before being blended with portland cement.
However, the prior art does not appear to disclose, suggest or otherwise motivate a person of ordinary skill in the art to provide a blended pozzolan composition comprised of calcium silicate and at least one waste byproduct of a glass material or glass product production processing process. In particular, the prior art lacks any teaching or motivation to provide a pozzolan composition which comprises calcium silicate, itself a waste byproduct of the production of elemental phosphorous, with cullet glass recovered from a glass-making facility and/or fused silica recovered from the process of making high purity refractory grade-fused silica. The prior art also lacks pozzolanic cements in which a pozzolan composition of the aforementioned makeup is admixed with a portland cement.